i comes down to energy, eating or expending energy through many things but especially exercise. the question is what causes some people to eat too much energy or not expend enough and how can we reverse that. that's what we're trying to figure out. >> behavioral. >> it's partly bavlt, partly physiological and biochemical. but how we get people to expend more energy and take in less is a tough question. >> the second thing you say is small sustained calories you take in will accumulate to burn large weight gain, why is that a myth? >> what happens is people have previously projected things would accumulate. for example, one of us started walk 30g minutes per day after dinner. that would expenld 100 calories a day. over 35 days that's 3,500 calories. one might think that would burn a pound of fat. 20 years you'll each have lost 100 pounds which is unrealistic because as you get smaller your body takes much less energy to move you from space and pump blood through your body and you reach a stable point. >> and number three, losing quickly is not as sustained as -- >> it sounds so r